Research On Aerodynamic Loads And Rigid-Flexible Coupling Dynamic Response Of Offshore Floating Wind Turbine

Under the background of global warming,the development of renewable energy is necessary.Offshore wind power is widely concerned for its outstanding advantages over onshore wind power.With the gradual maturity of offshore wind power technology,offshore wind farms show a trend of development from offshore to deep sea.Therefore,offshore floating wind turbine becomes the hot spot of offshore wind power technology research.The ocean environment is extremely complex,and the floating wind turbine is subjected to complex and variable wind,wave and flow loads at any time,and the loads are coupled to each other.In this paper,base on the classical blade element momentum theory,an unsteady aerodynamic loads simulation program is coded,taking into account the aerodynamic correction model,including wind shear and tower shadow effect,dynamic stall model and wake flow tilt model.The floating foundation hydrodynamic loads are solved based on the three-dimensional potential flow theory,and the mutual coupling between the two is studied.The results show that the floating foundation hydrodynamic loads play a great influence on the aerodynamic loads,and the wave frequency is dominant in the aerodynamic loads frequency.The structure of offshore floating wind turbine system is very complex.Based on the multi-body dynamics theory,this paper establishes the rigid-flexible coupling multi-body dynamics model of offshore floating wind turbine.According to the theory of continuous medium mechanics,the uniform mass finite element method(FEM)is adopted to discretize the flexible structure of multi-body system.Based on the Jourdain velocity variational principle and the first approximation modeling theory,the rigid-flexible coupling multi-body dynamic equations are derived.The MATLAB program is coded to achieve the rigid-flexible coupling of multi-body dynamics equations derivation and solution.Taking NREL OC4-DeepCwind offshore floating wind turbine system as an example,the free decay characteristics of foundation,natural frequency of tower,natural frequency of blade,aerodynamic characteristics of wind wheel and "dynamic stiffening" of rotating blade are calculated and analyzed through the program in this paper.Under the combined action of wind and waves,the influence of the secondary coupling term of the axial deformation of the blade,the influence of the second-order effect of wave loads and the coupling response of the floating wind turbine system are studied.The results show that the dynamic stiffness of the rotating blade increases with the increase of rotation speed,which affects the deformation of the blade.The aerodynamic performance of the wind turbine is significantly affected by the foundation,and the response frequency of output power and thrust is mainly based on the motion frequency of the foundation.The second-order wave forces have a great influence on the dynamic response of the floating foundation.The aerodynamic loads have little effect on the motion amplitude of floating foundation,which mainly causes the displacement of the balance position of foundation motion.